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Definitions and Terminology Modified Atmosphere Packaging (MAP) “ It is a form of packaging involving the removal of air from the pack and the replacement with single gas or mixture of gases” (Parry, 1993). Vacuum Packaging (VP) VP is also a type of MAP system because air is evacuated from a pack and not replaced and then the package sealed

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Gases used in modified atmosphere packaging Oxygen (O 2 ) stimulates the growth of aerobic bacteria and inhibits the growth of the strictly anaerobic bacteria presence of oxygen can cause oxidative rancidity in fatty fish low levels might induce browning reactions low level oxygen inhibit the growth of pathogenic anaerobic bacteria such as C. botulinum, Clostridium perfringens Carbon dioxide (CO 2 ) not inert and can bring about chemical changes in the microbial cell and its environment highly soluble in both water and lipids 25% CO 2 is recommended to control bacterial and mould growth most effective in reducing the growth of aerobic and Gram-negative psychrotrophic bacteria negative effects of CO 2 on the colour of fish, the texture of fish and drip loss high concentrations of CO 2 cause excessive drip, metallic and sour off-odors and off-flavors

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Gases used in modified atmosphere packaging Nitrogen (N 2 ) an inert and tasteless gas with a low solubility in both water and lipid delaying oxidative rancidity and inhibiting the growth of aerobic microorganisms filler gas to prevent pack collapse due to its low solubility Carbon monoxide (CO) highly toxic gas and is not approved by the regulatory authorities heath hazard for packaging machine operatives as well The other gases Potential gases: chlorine, ethylene oxide, nitrogen dioxide, ozone and sulphur dioxide unlikely to meet regulatory authorities approval due to safety concerns Noble gases: xenon, argon and helium permitted as food grade gases by EC legislation

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Effects of MAP on Clostridium botulinum Clostridium botulinum the single most important concern for MAP potential for the outgrowth and toxin production non-proteolytic, psychrotrophic (grow at a low as 3.3 o C) grow and produce toxin without producing over sign of spoilage Recommendation for controlling the growth of Clostridium botulinum (Betts, 1995) a heat treatment of 90 o C for 10 min or equivalent a pH value of 5 or less a minimum salt level of 3.5% NaCl in the aqueous phase an water activity of 0.97 or less throughout all parts of food a combination of heat and preservative factor or components Potassium sorbate, sodium chloride, nisin and irradiation in combination with MAP are shown to be effective

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Potential problems of MAP and VP Pack collapse Pack collapse occurs CO 2 permeates through packing films up to 30 times faster than N 2 fat and water-soluble solubility increases when temperature decreases To minimise pack collapse reducing CO2 content, increasing the product to gas ratio, injecting gas with a slight overpressure, pre-treating products with CO 2 saturated water or bicarbonate solutions pack in air Increased exudates/drip loss Fish loses about 1-3 % drip during normal storage Drip levels up to 14 % have been found for prawns decrease in water holding capacity of proteins due to a decrease in pH

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Potential problems of MAP and VP Discoloration the precipitation of sarcoplasmic proteins at low pH fading and browning have been attributed to packing in 100 % CO2 Histamine production produced by microbial decarboxylation of histidine numerous different bacterial species to possess histidine decarboxylase activity Vibrio, Proteus, Morganella morganii, Klebsiella pneumoniae, Hafnia alvei, etc. FDA legal limit: 5mg/100g fish (1996) EEC limit for histamine:10mg/100g fish (1991) TMA production TMA is produced only in fish in which contain adequate amounts of TMAO TMA production has been shown to be inhibited by MAP released when the consumer opens the pack

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Advantages and disadvantages of MAP Advantages of MAP Increased shelf life of products High quality products and reduced economic loss Products can be distributed longer distances, resulting in a decrease in distribution cost Clear view of products Hygienic stackable pack, sealed and free from product drip Disadvantages of MAP Visible added cost, for example; cost of gases and packing materials Temperature control required Specialized training and equipment are necessary Different gas formulation required for each product type Potential growth of food-borne pathogens such as C. botulinum Benefits of MAP are lost once the pack is opened